1. Field of the Invention
The invention relates to a pin and swaged tubular member type of fastener. Such fasteners are commonly used for securing together two or more workpieces, such as metal panels, having aligned holes through which the fastener is inserted.
There are two varieties of such fasteners. In the first variety, the pin has a radially enlarged head at one end, which head abuts one outside face of the workpieces, the pin shank extends through the holes and protrudes from the other outside face of the workpieces, and the tubular member is swaged on to the protruding part of the pin to abut that other face of the workpieces and lock the tubular member to the pin. Such fasteners are commonly known as lockbolts, and access to both sides of the workpieces is necessary to install the fastener.
The second variety of fastener requires access to only one side of the workpieces, and is therefore known as a blind fastener. In this variety of fastener the tubular member has an enlarged head at one end which head abuts the nearer outside face of the workpieces, with the tubular member extending through the aligned holes and protruding beyond the remote or blind outside face of the workpieces. The pin extends inside the tubular member and engages it at or near the end of the tubular member remote from the head thereof. Commonly (but not necessarily) the pin has an enlarged head which engages the tubular member. Such head is usually of a diameter no greater than that of the tubular member to facilitate the insertion through the aligned holes, and the filling thereof, by the tubular member. Instead of the pin having an enlarged head, the tubular member may be crimped into a groove in the pin. The pin is pulled to cause the remote end of the tubular member to enlarge radially and to form a blind head which abuts the remote or blind face of the workpieces. The head end of the tubular member is then swaged on to the pin, to lock the pin to the tubular member.
The present invention was developed primarily for application to the first variety of fastener, i.e. to lockbolts, and will hereinafter be described in detail in relation to lockbolts. However, it is equally applicable to blind fasteners of the second variety described above.
In order that the tubular member can be swaged to the pin, the pin is provided with a number of annular grooves (the locking grooves) into one or more of which the tubular member can be swaged by means of an annular anvil which engages the exterior of the tubular member, to lock the tubular member to the pin. Commonly an installation tool is employed in which the tail end of the pin extends through the annular anvil where it can be gripped by a gripping device (such as a set of jaws) incorporated in the tool, which also includes pulling means for pulling the gripping means against a reaction taken up through the anvil on to the tubular member.
In order that the gripping means can grip the pintail, the pintail is usually provided with a number of annular grooves (the pulling grooves) with which the gripping means can engage to pull the pin.
Since it is a practical requirement that, after completion of the swaging operation, the pin breaks at a position substantially level with the outside end of the swaged tubular member (the socalled "flush break" condition), the pin has commonly been provided with a breakneck, defined by an annular breakneck groove around it, and positioned, along the length of the pin, intermediate the locking grooves and the gripping grooves. The breakneck must be the weakest part of the pin, so that the breakneck groove must be deeper than any of the locking grooves and gripping grooves.
The provision of a single breakneck groove which must be aligned substantially level with the outside end of the swaged collar, in order to achieve a flush break, places severe limitations on the range of total thicknesses of workpieces (known as the "grip range") which identical fasteners of the same design can satifactorily join.
A grip range which is as large as possible is a very valuable practical advantage for such fasteners. Consequently there have from time to time been proposals to leave out the single breakneck groove and instead provide a number of combination grooves, each of which is capable of acting as either a locking groove or a breakneck groove, and which are arranged so that the pin will break at that one of those grooves which is substantially level with the outer end of the swaged tubular member. This provides a range of possible positions for the tubular member when it is swaged to the pin, but it has proved difficult in practice to ensure that pin-break occurs consistently at or near the outer end of the collar.
One proposed solution to this problem has been to apply a sideways or bending force to the pin tail after swaging is complete, but this requires the installation tool and/or fastener to be specially modified. Another solution proposed has been to provide combination locking-and-breakneck grooves which are of different cross-sectional shape at different positions along the pin. However this can be difficult to manufacture reliably, partially due to practical limitations of the rolling process by which such pins are commonly manufactured. Furthermore, there must be significant differences between each such groove and the next, for such a system to be effective. These differences are of course cumulative along successive grooves, and the distance apart of the limiting cases of cross-sectional shape of groove which will function properly as both locking groove or breaker groove is the limit of the increase in grip range.
It has also been found in practice that it is desirable to maintain the dimension of the diameter of the breakneck below a certain ratio to the dimension of the pitch of the grooves (i.e. the distance between adjacent breaknecks). With prior art forms of combination locking and breakneck grooves this has presented difficulties, since increase in the maximum depth of the grooves whilst keeping the pitch the same would result in a shape of groove cross-section which may reduce the effectiveness of the lock between swaged collar and the pin, thus weakening the tension strength of the joint produced.
These problems would be made even more difficult if it were desired to provide a single design of groove cross-section which could also act as a pulling groove, so that each groove is a combination locking, breaking and pulling groove.